An Investigation into the Relationship between Surface Rain Rate and Rain Depth over Southeast Asia

The relationship between surface rain rate and depth of rain system （rain depth） over Southeast Asia is examined using 10-yr Tropical Rainfall Measuring Mission （TRMM） precipitation radar （PR） measurements. Results show that, in general, a large surface rain rate is associated with a deep precipitating system, but a deep rain system may not always correspond with a large surface rain rate. This feature has a regional characteristic, Convective rain develops more frequently over land than over the ocean, while stratiform rain can extend to higher altitudes over the ocean than over land. A light surface rain rate has the largest probability to occur, regardless of rain depth. A convective rain system is more likely associated with a stronger surface rain rate than a stratiform rain system. Results show that precipitation systems involve complex microphysical processes. Rain depth is just one characteristic of precipitation. A linear relationship between surface rain rate and rain depth does not exist. Both deep convective and stratiform rain systems have reflectivity profiles that can be divided into three sections. The main difference in their profiles is at higher levels, from 4.5 km up to 19 km. For shallow stratiform rain systems, a two-section refiectivity profile mainly exists, while for convective systems a three-section profile is more common.

Climatic characteristics of convective and stratiform precipitation over the Tropical and Subtropical areas as derived from TRMM PR

Climatic characteristics of convective and stratiform precipitation over the Tropical and Subtropical areas are investigated based on the measurements of Tropical Rainfall Measuring Mission's(TRMM) Precipitation Radar(PR) from 1998 to 2007.Results indicate that convective precipitation are distributed mainly over the Intertropical Convergence Zone(ITCZ),the South Pacific Convergence Zone(SPCZ),the Asian Monsoon Region,regions between the South America and the Mid-America,and the Tropical Africa where the frequencies lie between 1% and 2%.But in four seasons,total area fractions of convective precipitation frequencies less than 1% all exceed 85%.The frequencies of stratiform precipitation are much higher than those of convective precipitation,and total area fractions of stratiform precipitation frequencies >1% are over 55% during four seasons.However,frequencies of the two rain types show not only remarkable regionality,but also distinct seasonal variations.Conditional rain rates of convective precipitation range from 6 to 14 mm/h whereas those of stratiform precipitation are smaller than 4 mm/h.Meanwhile,rain tops of convective precipitation are higher than those of stratiform precipitation.The mean profiles of the two rain types show significant latitudinal dependency.And the seasonal variations of precipitation profiles are displayed mainly in the variations of rain tops.The frequencies and conditional rain rates of both rain types over ocean are higher than those over land,but rain tops are just the opposite.Moreover,the seasonal variations of both rain types over ocean are weaker than those over land because of the different stable states of underlying surfaces.

The Seasonal and Interannual Variation of Diurnal Precipitation over the Tibetan Plateau and Its Downstream Regions Observed by the Tropical Rainfall Measuring Mission

Using nine years of Tropical Rainfall Measuring Mission(TRMM)2A25 data,based on the probability density function of rainfall,a comparative analysis of the diurnal cycle and its seasonal and interannual variation for convective rain,stratiform rain,and total rain is made between the Tibetan Plateau and the downstream Yangtze River basin and East China Sea.The diurnal convective rain is stronger than the diurnal stratiform rain over the Yangtze River basin,and the convective rain peaks in the afternoon when the stratiform rain maximum happens in the early morning.Convective rain and stratiform rain both peak in the early morning over the East China Sea.The diurnal total rain over the Tibetan Plateau is stronger than its downstream regions.The diurnal cycle appears quite different among the four seasons over the Yangtze River basin,and the seasonal variation of diurnal convective rain is more apparent than diurnal stratiform rain.The seasonal variation of the diurnal cycle is weak over the East China Sea and Tibetan Plateau.The maximum of total rain happens in the afternoon during1998–2002 over the Yangtze River basin,while it peaks in the early morning during 2003–2006,but no obvious phase differences can be found among years in the diurnal rain over the East China Sea and over the Tibetan Plateau.

Understanding the Variability of Z-R Relationships Caused by Natural Variations in Raindrop Size Distributions(DSD):Implication of Drop Size and Number

In the issue of rainfall estimation by radar through the necessary relationship between radar reflectivity Z and rain rate R (Z-R), the main limitation is attributed to the variability of this relationship. Indeed, several pre-vious studies have shown the great variability of this relationship in space and time, from a rainfall event to another and even within a single rainfall event. Recent studies have shown that the variability of raindrop size distributions and thereby Z-R relationships is therefore, more the result of complex dynamic, thermody-namic and microphysical processes within rainfall systems than a convective/stratiform classification of the ground rainfall signature. The raindrop number and size at ground being the resultant of various processes mentioned above, a suitable approach would be to analyze their variability in relation to that of Z-R relation-ship. In this study, we investigated the total raindrop concentration number NT and the median volume di-ameter D0 used in numerous studies, and have shown that the combination of these two ‘observed’ parame-ters appears to be an interesting approach to better understand the variability of the Z-R relationships in the rainfall events, without assuming a certain analytical raindrop size distribution model (exponential, gamma, or log-normal). The present study is based on the analysis of disdrometer data collected at different seasons and places in Africa, and aims to show the degree of the raindrop size and number implication in regard to the Z-R relationships variability.

Diurnal Variability of Precipitation Depth Over the Tibetan Plateau and Its Surrounding Regions

The diurnal variability of precipitation depth over the Tibetan Plateau and its surrounding regions is investigated using nine years of Tropical Rainfall Measuring Mission （TRMM） precipitation radar （PR） measurements. The Tibetan Plateau, the plains area, and the East China Sea are selected as the focus regions in this study. The average precipitation depths （PD） are about 4.6 km, 5.8 km, and 5.6 km, while convective （stratiform） PDs are about 6.6 （4.5） km, 7.5 （5.7） km, and 6.0 （5.6） km over the plateau, the plains, and the ocean region, respectively. Results demonstrate a prominent PD diurnal cycle, and its diurnal phase is generally a few hours behind the surface precipitation. The spatial variation of the PD diurnal magnitude is weaker near the coastal areas than that of surface precipitation. The height of the PD diurnal peak is around 6 7 km for convective systems and 5-6 km for stratifrom systems. The dominant afternoon diurnal peak for convective PD and the flat diurnal peak for stratiform PD over the Tibetan Plateau indicate that solar diurnal forcing is the key mechanism of the PD diurnal cycle over land. In addition, the diurnal variation is obvious for shallow and deep convective systems, but not for shallow and deep stratiform systems.

基于雨滴谱和雨量筒观测资料不同类型云降水对比分析

选取北海国家气候观象台2019年1—12月的雨滴谱和雨量筒资料,根据雨强划分降水类型,对比分析两种设备观测对流云和层状云降水的差异。结果表明:(1)两次降水过程均以“雨”和“阵雨”为主,由于仪器测量精度不同,雨滴谱和雨量筒观测到的降水量有所差别。(2)对于对流云和层状云降水,雨量筒与雨滴谱累积降水量绝对误差均小于20%,相关性系数均达到0.99;另外,对流云事件雨滴谱与雨量筒累积降水量平均值误差大于层状云事件的。(3)雨滴谱仪观测出现降雨时间早于雨量筒记录的,降雨结束时间则晚于雨量筒记录的。相比于层状云降水,对流云降水起始阶段雨量更大,降雨速度更快,雨滴谱仪和雨量筒记录到有降水现象的时间差更小。

冬、夏季热带及副热带穿透性对流气候特征分析

文中利用热带测雨卫星(TRMM)搭载的测雨雷达(PR)1998～2007年的探测结果,就热带及副热带地区穿透性对流的频次、条件降水强度及垂直廓线等特征进行了分析。研究结果表明:深对流和穿透性对流都主要发生在热带辐合带(ITCZ)、南太平洋辐合带(SPCZ)、亚洲季风区、20°N以南的非洲以及美洲等地区,它们的空间分布具有明显的地域性和季节变化特征,而且陆地深对流更容易发展成为穿透性对流,但绝大部分地区的穿透性对流频次不超过0.2%。对穿透性对流条件降水强度的分析表明,热带及副热带大部分地区的穿透性对流条件降水强度在10mm/h以上,且洋面的条件降水强度要比陆地大,但由于其频次较小导致其对总降水的贡献并不大。尽管深对流和穿透性对流降水廓线的外形比较相似,但相同的高度,深对流的降水强度要比穿透性对流偏小,而且这种差异随海陆和纬度的不同而有所区别。此外,热带地区(15°S～15°N)冬、夏季深对流和穿透性对流降水廓线都只存在较小差异,并没有显示出明显的季节变化。

“碧利斯”(0604)暴雨过程不同类型降水云微物理特征分析

本文利用"碧利斯"(0604)暴雨增幅过程高分辨率的数值模拟资料,将降水分成对流降水和层云降水,对比分析了不同类型降水云微物理特征和过程的差异,探讨了不同类型降水对暴雨增幅的贡献,结果指出:(1)暴雨增幅前,降水基本为层云降水,对流降水只存在于零星的几个小区域,暴雨增幅发生时段,对流降水所占比例较暴雨增幅前有显著增加,平均降水强度达层云降水强度的3倍多。(2)暴雨增幅时段,云系发展更加旺盛,云中各种水凝物含量较增幅前明显增加,其中,对流和层云降水区云中水凝物含量均有一定程度增长,但对流降水区增加更显著;而无论增幅前还是增幅时段,对流降水区云中水凝物含量均要明显大于层云降水区,并且两者的这种差异随着地面降水强度的增强而增大。(3)暴雨增幅前后,对流降水区雨滴的两个主要来源最终均可以追踪到云水,通过云水与大的液相粒子(雨滴)和大的固相粒子(雪)之间、以及大的固相粒子(雪和霰)之间的相互作用和转化,造成雨滴增长,并最终形成地面降水,而层云降水区中与雨滴形成相关的上述主要云微物理过程明显变弱,但层云降水区中暴雨增幅时段的上述过程又要强于增幅前,说明层云降水对暴雨增幅也有一定贡献。

利用星载测雨雷达探测结果对夏季中国南方对流和层云降水气候特征的分析

本文利用热带测雨卫星(TRMM)上搭载的测雨雷达(PR)十年的探测结果,对夏季中国南方对流降水和层云降水的气候特征进行了分析。研究结果表明:夏季中国南方层云降水频次较对流降水频次高出两倍以上,而对流降水强度至少是层云降水强度的4倍;就整个中国南方而言,这两种类型的降水对总降水量贡献相当。日变化分析表明夏季中国南方大部分地区的对流降水主要出现在午后,层云降水出现时间并不集中,但这两类降水的频次日变化均显示了明显的地域性特征;对降水廓线日变化的分析结果表明,对流降水和层云降水廓线的日变化主要表现在"雨顶"高度的日变化,即对流降水云的厚度有明显的日变化变化特征,不同地区的降水廓线存在明显的差异。降水率剖面分析结果显示了对流降水的"雨顶"高度日变化较层云降水剧烈,降水率的日变化则相反,且层云降水率的地域性特征更强。

2002年7月沈阳一次降水过程的催化数值模拟研究

应用三维对流云模式和探空资料,对沈阳地区2002年7月12日发生的一次东北冷涡降水过程进行了数值模拟研究。结果表明,这次降水主要是由积层混合云引起的,其中冰相过程占主导地位,霰的融化是最主要的雨生成项。催化模拟试验表明,当云体处于成熟稳定的积层混合云阶段,在0℃层高度以上播撒AgI能起到显著的增雨效果。积层混合云具有巨大的人工增雨潜力。

地形对山西垣曲“0729”特大暴雨影响的数值模拟分析

利用WRF-ARW中尺度数值模式,对山西南部垣曲县喇叭口地形造成的"0729"特大暴雨过程进行了数值模拟和地形敏感性试验,通过分析暴雨云团的动力和微物理结构,探讨地形激发积层混合云系的结构特征及地形对暴雨云系的影响。结果表明:西风带系统与副热带系统相向而行是此次暴雨发生的环流背景特征,当中低空受偏南风急流影响时,垣曲县向南开放的喇叭口地形可使低层的辐合上升显著增强。特殊地形所激发的meso-β积层混合云团是造成此次特大暴雨的直接系统。地形敏感性试验结果表明:地形的变化对积层混合云系的动力结构、微物理特征等有显著影响。地形降低后,喇叭口效应形成的低层强辐合结构与强上升气流消失;下风方向低层辐合、中高层辐散配合强烈的上升运动,对流发展趋于旺盛,暴雨中心向地形下游移动。地形的变化对水相物质的微物理结构也有显著的影响。地形降低后,迎风坡上空上升运动减弱,进入到中间层上层的云水粒子减少,凝华生成的冰晶粒子减少,"播撒—供给"机制减弱,迎风坡降水强度明显减弱;下风方向对流加强,更多的云水粒子进入到中间层上层,降水强度加强。喇叭口地形的存在更有利于上游强对流发展并形成层积混合云系,对下游对流起抑制作用。

基于偏振雷达的积层混合云降水增雨潜力识别方法研究

本文统计分析了北京地区近三年的有效降水,重点研究了积层混合云降水特点并对其分类,发现积层混合云降水出现频次约占总降水次数的61%,其中积层混合云降水以积层连结型和水平混合型为主,二者之和占近80%。重点分析了积层混合云中对流和层云两种不同特点降水类型的宏微观结构,确立了反射率因子Z、温度T、粒子含水量M、催化剂AgI(碘化银)活化率NE和粒子相态HTC(hydrometeor type classification)为人工增雨潜力识别指标及这些识别指标的取值范围,同时也根据研究现状和人工影响天气需求总结制定出人工增雨潜力等级。利用偏振雷达构建模糊逻辑识别算法对积层混合云三种降水类型进行增雨潜力区域识别研究,结果表明:(1)对于播撒碘化银增雨来说,积层混合云的增雨潜力区在垂直方向上可分为上、中、下三层,上层(增雨等级为"不适合")和下层(零度层及以下)分别受含水量和温度等影响不适合增雨,中间层(增雨等级大于等于"等级一")是可增雨区域;(2)积层混合云中层云区增雨潜力较小,对流云区可增雨潜力要远大于层云区,开式流场型与积层连结型可增雨潜力要大于水平混合型;(3)当降水云中识别出霰粒子时,其附近的大部分区域会有较好的增雨潜力。通过偏振雷达实例检验和数值模式模拟在积层混合云不同部位播撒碘化银催化试验发现,在增雨潜力较好的区域催化有很明显增雨效果,模拟试验结论与偏振雷达识别增雨潜力区结果也基本一致,说明基于偏振雷达的增雨潜力区识别方法和结果是具有参考意义的。

山东不同云系降水微物理参数特征

研究不同云系降水的微物理参数特征,对研究降水机制、人工影响天气、雷达定量测量降水、数值预报模式中微物理参数化方案的选择等都有一定意义。本文针对2015年济南地区的液态降水过程,基于微降水雷达(Micro Rain Radar,简称MRR)资料,研究不同云系降水的微物理参数。在400 m高度上,层状云降水0.02~0.2 mm h-1雨强样本数很大,但对累计降水量的贡献很小。混合云和对流云降水在大粒子端数浓度较高。在垂直方向上,层状云降水中的粒子的尺度较集中,中值体积直径D0平均在1 mm左右,随高度的变化不大。对流云降水在雨强大于20 mm h-1时,强垂直气流(包括上升气流和下沉气流)对粒子直径的影响较大,进而影响空中微降水雷达反演降水参数的数据质量。而垂直气流的影响对层状云降水影响较小,在层状云降水时,微降水雷达可以用来分析零度层亮带以下雨滴谱在垂直方向上的演变。

2014年南京青奥会开幕式日降水过程数值模拟研究

为评估2014年南京青奥会开幕式日的人工催化消减雨作业效果,利用中尺度数值模式WRF对当日的云降水过程和催化作业开展数值模拟。本文系第一部分工作。首先对常用的八种云微物理方案的降水模拟效果进行评估,进一步选取Thompson和Milbrandt-Yau两个微物理方案对此次降水过程的云系结构和降水形成机制进行对比分析。模拟结果表明,采用Thompson和Milbrandt-Yau两个方案模拟的云系结构和降水形成的微物理机制是一致的。开幕式当天影响奥体场馆的降水由弱的积层混合云系产生,降水过程以冰相微物理过程为主。雪的融化是雨水的主要源项,Thompson方案中雪的融化对雨水的贡献率为72%,Milbrandt-Yau方案为60%,蒸发则是雨水的主要汇项,Thompson方案中蒸发对雨水的消耗率达94%,Milbrandt-Yau方案为95.6%。

四川省稻城地区雨滴谱特征研究

利用四川稻城地区2019年5~8月雨滴谱资料,研究不同雨强和不同降水的雨滴谱特征,并提出反射率因子Z、质量加权平均直径D_(m)粒、粒子总数浓度N_(T)、含水量W与雨强R之间的关系,以及Gamma谱形状参数μ和斜率参数Λ之间的关系,并比较了该地区雨滴谱与我国其他地区的差异。结果表明:随着R增大,雨滴谱数浓度、粒径和谱宽也逐渐增大,雨滴谱逐渐变宽、变平坦;对流云雨滴谱明显比层状云宽、数浓度更高,谱型分别呈略微的上凸和下凹;W-R和Z-R幂函数关系最密切,其次为D_(m)-R和N_(T)-R,μ-∧很好符合二项式关系;稻城地区的D_(m)和截距参数Nw与其他区域不同,D_(m)仅大于亚洲季风区江淮流域,而N_(w)仅比华北地区大。

青藏高原东南部不同地区的雨滴谱特征研究

利用2019年5~8月青藏高原东南部石渠、新龙和泸定站雨滴谱资料,在对比分析3个地区不同雨强和不同降水类型雨滴谱特征的基础上,确定了降水的反射率因子–雨强(Z–R)关系和谱形状–斜率(μ–Λ)关系,探讨了高原东南部与我国其他地区雨滴谱的差异。结果表明:青藏高原东南部地区雨滴数浓度随雨强增大而上升,石渠在相同雨强下可以产生少量更大的雨滴,中大雨滴的数浓度由大到小依次为石渠、新龙、泸定。Gamma模型对青藏高原东南部层状云和对流云降水雨滴谱的模拟效果均较好,对流云降水雨滴谱明显较层状云降水更宽且斜率更小。层状云降水Z–R关系基本一致,而对流云降水在相同R下对应的Z值由大到小依次为石渠、新龙、泸定;μ–Λ关系也基本一致,符合二项式关系。青藏高原东南部层状云和对流云降水中的平均N_(w)小于国内其他地区,其中,石渠对流云降水的平均D_(m)最大而平均N_(w)最小。